The aquatic plant Azolla filiculoides was grown in nine
tanks of total area 468 m² and fed as partial replacement (0, 15
and 30%) of the protein in a soyabean-based supplement given in
restricted quantities (200 g protein/animal/daily) with fresh
sugar cane juice to growing-fattening pigs. The trial was done on
a commercial farm in the Valle del Cauca in Colombia (1000 m
above sea level; mean temperature 24°C and rainfall 1100 mm).

The recorded productivity of the Azolla during the 5 month
period of the trial was high (equivalent to 9 tonnes
protein/ha/year). In the growing phase, pig performance decreased
as the amount of Azolla in the diet increased. These effects were
reversed in the fininishing phase when there was a strong
tendency for the pigs fed azolla to grow faster than on the
control treatment. The final result was that there were no
differences in growth rate among treatment groups for the total
period of the trial (from 24 to 89 kg liveweight).

This preliminary information has served to stimulate interest
in the growing and use of Azolla as a protein supplement in
Colombia. The technology is already being applied on a number of
farms with satisfactory results both from the biological and
economic standpoint. More importantly, these on-farm activities
are generating invaluable information concerning the practice of
growing and utilization of this feed resource under varying
environmental conditions.

One of the principal limiting factors to profitability of a
pig enterprise using sugar cane juice as the basal diet is the
cost of the protein supplement. Two approaches have been
investigated to combat this problem. The first is based on the
report of Estrella et al (1986) (cited by Mena 1989) that
the protein input (mainly soyabean meal) to pigs fed ad
libitum cane juice during the finishing phase (76 to 105 kg)
could be reduced to 180 g/animal/d without affecting growth rates
(780 g/d with 180 g protein/d compared with 820 g/d with 360 g
protein/d). Based on this data, the present recommendations of
CIPAV for sugar cane juice feeding systems are that the protein
allowance be set at 200 g/d and maintained constant throughout
the growing-fattening phase (Sarria 1989).

The second approach aims to take advantage of the absence of
fibre in sugar cane juice so as to be able to accomodate foliar
sources of protein in the form of leaves harvested from forage
crops, trees and water plants. Mena (1989) cited observations by
Abreu et al that fresh leaves from both cassava and
leucaena were consumed by pigs fed on cane juice and restricted
amounts of protein supplement. Growth rates appeared to be
reduced by leucaena but not by cassava leaves. One of the
problems with leaves from tropical tree species is the presence
of secondary plant compounds, chiefly phenolic substances, whose
role is to protect the leaf from insect attack. Unfortunately,
another characteristic of these substances is that they make the
leaf unpalatable, especially for monogastric animals. Thus leaves
of Gliricidia sepium , although readily eaten by
ruminants, are not relished by either chickens or pigs.

Aquatic plant species, because of their growth habit, appear
not to accumulate secondary plant compounds and therefore offer
perhaps a greater potential than trees as a source of protein for
monogastric animals. Of these species the water fern Azolla
filiculoides, which grows in association with the blue-green
alga Anabaena azollae, is perhaps the most promising from
the point of view of ease of cultivation, productivity and
nutritive value (Lumpkin and Plucknett 1982; Van Hove and López
1983).

The aims of the experiments to be described in this paper were
to obtain data under commercial farm conditions concerning: (i)
the management and productivity of Azolla as a protein crop; and
(ii) its value as a partial replacement for soyabean meal in a
sugar cane juice feeding system for pigs.

Materials and methods

The experiments were carried out on the "Lucerna"
farm situated near the town of Bugalagrande (latitude 3°N and
longitude 76°E) Departamento Valle del Cauca. Height above sea
level is 960 m, mean temperature 24°C (range 19 to 29°C) and
mean rainfall 1100 mm. Relative humidity varies from 60 to 85%
throughout the year.

Production of Azolla

Nine tanks were constructed each measuring 20 m long, 2.6 m
wide and 0.7 m deep with a 2 m separation between each giving a
total surface area of 468 m². They were sown with a culture of Azollafiliculoides of Brazilian origin which was growing on a
commercial farm also situated in the Valley but at some 1500 m
above sea level. Fertilization was with poultry litter at the
rate of 10 g/m²/d. Water depth was maintained at 40 cm using
river water. The amount added to compensate for evaporation and
filtration corresponded to approximately 5% of the total volume
daily. Each day 100 kg fresh weight of Azolla was harvested,
corresponding to the production of one quarter of the area of
three tanks. Thus there was an interval of three days before
returning to harvest the same tanks.

Pig feeding experiment

Treatments, experimental design and analysis

Three dietary treatments were imposed on growing-fattening
pigs receiving a basal diet of fresh sugar cane juice. These
consisted of:

Azolla 15: 425 g/animal/d of the protein supplement and
2.6 kg/animal/d of fresh Azolla (providing 15% of the
total protein allowance)

Azolla 30: 350 g/animal/d of the supplement and 5.2
kg/animal/d of Azolla

A homogeneous group of 13 weaner pigs was allocated to each
treatment. The pens were adjacent to one another and of similar
size. Statistical analysis was restricted to the liveweight data,
using differences among animals within pens as the source of
residual variation. The data were analysed separately over the
growth phase (20 to 50 kg liveweight), the fattening phase (50 to
90 kg) and the overall period.

Pigs and diets

The weaner pigs weighed 20 kg on average at the start of the
trial. The conventional protein supplemented was prepared on the
farm and contained 90% soybean meal and 10% of a mineral-vitamin
mixture. It was given as the first feed in the morning at
approximately 7 am, followed by the azolla which had been
harvested the day before and left to drain overnight. Fresh cane
juice was extracted from the stalks of sugar cane grown
commercially on the farm (some 300 ha are established on the farm
for sale to the local sugar factory) using a 3-roll mill
(capacity about 1 tonne cane stalk/hour), typically employed for
production of "Panela" (non-crystallized brown sugar).
Extraction rate averaged 50 kg of juice from 100 kg of cane
stalk. The cane juice was given first at approximately 11 am
(immediately after milling of the stalk) and again in the
afternoon in quantities calculated to result in a slight residue
the following morning. Precise control of the amount of juice
offered and refused was not possible as the experimental groups
had to be managed as a component of the overall commercial
programme which involved some 200 animals all fed on the cane
juice system. The mean intakes were estimated to be about 7
litres daily in the growth phase and 11 litres in the finishing
phase. The pigs were weighed individually every 14 days and mean
liveweight gains calculated from the regression coefficient of
liveweight against time.

Results and discusion

Estimates of the annual productivity of the Azolla, assuming
the production during the first 150 days can be sustained, are
given in Table 1.

Table 1:
Estimated productivity of Azolla biomass based on actual
amounts harvested during the 154 days of the trial from 1
June to 31 October 1989.

Total area of
tanks (m²)

468

Azolla
harvested daily (kg)

- Total
amount fresh basis

100

- Total dry
weight

5

- Protein in
dry matter (%)

23

- Total
protein daily (kg)

1.15

Estimated
annual production (tonnes/ha)

- Dry biomass

39

- Protein

9.00

The recorded productivity of the Azolla during the 5 month
period of the trial was high and within the range (6 to 9 tonnes
protein/ha/year) reported by Lumpkin and Plucknett (1982).

Analysis of nitrogen, P, Ca and K in representative samples of
the Azolla from the experiment shows that the recorded values are
within the range reported in the literature (Table 2).

Table 2: Chemical
composition of the Azolla

Analysis % of
DM

Lucerna

Literature*

Nitrogen

3.8

2.0 - 5.3

P

0.7

0.2 - 1.6

Ca

1.7

0.5 - 1.7

K

1.8

0.3 - 6.0

* Source: Van Hove y Lopez (1983)

Mean values for liveweight gain and feed intake are given in
Tables 3, 4 and 5 for the growth, finishing and overall phases
respectively.

Table 5: Mean
values for growth rate, feed intake and feed conversion
during the overall period

%
protein replaced by Azola

Control

15

30

SE(Prob)

No of pigs

13

13

11

Liveweight
(kg)

- Initial

25.3

23.0

21.2

- Final

90.5

89.7

87.5

- Daily gain

0.482

0.475

0.454

±0.045(0.80)

Length of
period (d)

138

154

154

Feed
intake (kg/d)

- Cane juice

9.1

9.1

9.1

- Protein
supplement

0.5

0.425

0.35

- Azolla

-

2.6

5.2

- Dry matter

2.27

2.33

2.39

Conversion
(DM basis)

4.73

4.90

5.26

There were significant differences (P = 0.01) among groups of
pigs receiving the experimental treatments during the growth
phase (Table 3). Performance decreased as the amount of Azolla in
the diet increased. These effects were reversed in the
fininishing phase when there was a strong tendency (P = 0.2) for
the pigs fed azolla to grow faster than on the control treatment
(Table 4). The final result was that there were no differences in
growth rate (P = 0.80) among treatment groups for the total
period of the trial (Table 5).

It is understood that the differences attributable to the
treatments are confounded with the differences attributable to
pens since there were no replications of pens. However, the pens
were of similar size and design and located together in the same
part of the piggery. It seems reasonable to conclude that the
observed differences among treatments probably were the result of
the level of Azolla in the diet.

It is difficult to explain the contrasting differences in the
growing and fattening phases. A reasonable hypothesis would be
that the limiting factor to the use of fresh Azolla in the diet
of pigs is its low nutrient density due to the extremely high
moisture content (approximately 95%), and the inability of the
young pigs to consume the required quantities. This was observed
to be the case with fresh leaves from the tree Trichantera
gigantea which were consumed in adequate amounts (i.e. to
supply 200 g protein daily) by pregnant sows but not by growing
pigs (C. Mejia, personal communication). It did not seem that
this was the problem in the present experiment since the
indicated amounts were consumed fully. However, it was observed
that during the growing phase it was necessary to offer the
Azolla in two portions daily while in the finishing period it was
sufficient to feed it only once in the morning. More observations
are necessary before this theory can be substantiated or
rejected.

A possible imbalance of amino acids due to inclusion of Azolla
would not appear to be the problem, since Azolla protein appears
to have a better amino acid profile than soybean mean such that
the combination of the two more closely resembles the balance
required by the growing pig according to the recent studies of
Wang and Fuller (1989) (Table 6).

More logical explanantions for the diferences in utilization
efficiency of the Azolla according to the age (size) of the pig
are that some period of adaptation is necessary to develop a
microbial flora in the caecum capable of digesting efficiently
the fibrous components of this plant. Alternatively, the older
animal may masticate more thoroughly the plant material during
eating which would facilitate access to the Azolla protein by the
pig's gastric enzymes. The fact that performance tended to be
better with 15% than with 30% replacement by Azolla protein
supports this view.

Table 6: The
balance of amino acids (as % of Lysine = 100) required by
the growing pig (Wang and Fuller 1989)* compared with
that supplied by soybean meal (control supplement) and
combinations of soyabean meal and Azolla.

Optimum*

%
protein replaced by Azolla

Control

15

30

Lysine

100

100

100

100

Met+cis

63

48

50

53

Threonine

72

61

63

65

Tryptophan

18

22

23

25

Valina

75

83

86

89

Isoleucine

60

90

89

88

Leucine

110

133

134

135

Phenylan+Tyrosine

120

139

141

143

Relation
essential to non-essential AA

50:50

40:60

42:58

43:57

Conclusions

The preliminary data reported in this paper must be
interpreted in the light of the limitations facing most animal
experiments carried out on commercial farms, especially the
difficulty of obtaining precise data on feed intake and being
able to set up correctly designed trials with adequate
replications. Despite this, the information obtained has served
to stimulate interest in the growing and use of Azolla as a
protein supplement. The net result is that the technology is
already being applied on a number of farms in Colombia, with
satisfactory results both from the biological and economic
standpoint. More importantly, these on- farm activities are
generating invaluable information concerning the practice of
growing and utilization of this feed resource under varying
environmental conditions.

Acknowledgments

This experiment was carried out as part of the requirements
for the graduate thesis of the senior author. The authors
acknowledge the contribution of of the management and workers of
the Lucerna farm, and of the researchers in CIPAV, whose interest
and collaboration made this work possible.